A typical aromatics complex includes a xylene isomerization unit and a transalkylation unit. The xylene isomerization unit and the transalkylation unit are completely separate process units, each with its own separator, recycle gas compressor, and fractionation column.
An example of a current aromatics complex is shown in FIG. 1. The complex includes a xylene isomerization unit 5 and the transalkylation unit 10. The isomerization unit 5 has an isomerization reactor 15. The feed 20 is pre-heated in a heat exchanger 25 and further heated in a charge heater 30 before entering the isomerization reactor 15. The effluent 35 from the isomerization reactor 15 is sent to the heat exchanger 25, the condenser 37, and then to the separator 40. The overhead 45 from the separator 40 is sent to a recycle gas compressor 50 and is recycled back to the isomerization reactor 15. Make-up hydrogen 55 is added to the compressed overhead 45 as needed. The liquid 60 from the separator 40 is sent to a detoluene fractionation column 65. The overhead 70 is sent to the condenser 73, and the overhead receiver 75. The liquid 80 from the overhead receiver 75 is divided into a reflux stream 85 that is sent back to the detoluene fractionation column 65 and a net overhead stream 90 that is sent to a stripper column 95. The overhead 100 from the stripper column 95 is combined with the vapor 70 from the column 65 and recycled back to the condenser 73 and separator 75. Overhead vapor 105 is removed from overhead receiver 75 to maintain column pressure control. The bottoms 110 from the stripper column 95 is sent to a benzene column or to an aromatic extraction unit (not shown). The bottoms 115 from the detoluene fractionation column 65 is divided into stream 120, which is sent to the reboiler 125 and back to the detoluene fractionation column 65, and stream 130, which is sent to a xylene column (not shown).
The transalkylation unit 10 has a transalkylation reactor 135. The feed 140 is pre-heated in a heat exchanger 145 and further heated in a charge heater 150 before entering the transalkylation reactor 135. The effluent 155 from the transalkylation reactor 135 is sent to the heat exchanger 145, the condenser 157, and then to the separator 160. The overhead 165 from the separator 160 is sent to a recycle gas compressor 170 and is recycled back to the transalkylation reactor 135. Make-up hydrogen 175 is added to the compressed overhead 165 as needed. The liquid 180 from the separator 160 is sent to a detoluene fractionation column 185. The overhead 190 is sent to a condenser 193, and overhead receiver 195. The effluent 200 from the overhead receiver 195 is divided into a reflux stream 205 that is sent back to the detoluene fractionation column 185 and a net overhead stream 210 that is sent to a stripper column 215. The overhead 220 from the stripper column 215 is combined with the vapor 190 from the column 185 and recycled back to the condenser 193 and overhead receiver 195. Overhead vapor 220 is removed from overhead receiver 195 to maintain column pressure control. The bottoms 230 from the stripper column 215 is sent to a benzene column or to an aromatic extraction unit (not shown). The bottoms 235 from the detoluene fractionation column 185 is divided into stream 240, which is sent to the reboiler 245 and back to the detoluene fractionation column 185, and stream 250, which is sent to a xylene column (not shown).
The duplication of equipment, such as the separators, gas recycle compressors, and fractionation columns, to process streams containing similar components, although in different amounts, adds significant capital cost to the aromatics complex.